This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A368424 #27 Jan 25 2024 02:41:03 %S A368424 4,11,18,20,23,28,35,43,48,52,83,95,100,119,131,138,148,155,162,166, %T A368424 172,179,191,196,204,210,214,239,251,253,268,292,299,300,316,323,342, %U A368424 359,371,378,388,419,431,443,460,463,491,500,508,515,537,556,564,575 %N A368424 Numbers k such that gcd(A019320(k), A019321(k)) > 1. %C A368424 The corresponding greatest common divisors are given in A368425. %H A368424 Robert Israel, <a href="/A368424/b368424.txt">Table of n, a(n) for n = 1..1000</a> %e A368424 a(1) = 4 since A019320(4) = 5 and A019321(4) = 10. %p A368424 select(k -> igcd(numtheory:-cyclotomic(k,2), %p A368424 numtheory:-cyclotomic(k,3)) > 1, [$1..1000]); # _Robert Israel_, Dec 26 2023 %t A368424 Select[Range[600],GCD[Cyclotomic[#,2],Cyclotomic[#,3]]>1&] (* _Stefano Spezia_, Dec 26 2023 *) %o A368424 (PARI) for(n=1,1000,if(gcd(polcyclo(n,2),polcyclo(n,3))>1,print1(n,", "))) %Y A368424 Cf. A019320, A019321, A191609 (prime factors of such gcds), A368425. %K A368424 nonn %O A368424 1,1 %A A368424 _Tomohiro Yamada_, Dec 24 2023